Open wire transmission line



Patented Jan. 8, 1946 UNITED STATES PATENT OFFICE 2,392,473 OPEN WIRE ramsmssron mm Thomas M. Gluyas, Jr., Collingswood, N.=.F., asslgnor to Radio Corporation of America, a corporation of Delaware Application May 29, 1942,, Serial No. 445,039 7 Claims. (01- Hit-d ll This invention relates generally to transmission lines and particularly to means for reducing radiation from high frequency transmission lines caused by current Phase unbalance in the line.

It is well known that if the phases of the C111? rents in a two wire high frequency transmission line are not exactly in oppwition'that objectionable radiation will occur which is a function of the vector sum of the two currents. Such phase unbalance is inherent in most parallel wire transmission lines due to dissymmetry in the line,

generator or load circuits.

The invention contemplates eflectively neutralizing the phase unbalanceof a conventional parallel wire high frequency transmission line by utilizing a third wire disposed equidistant from each of the transmission wires, and applying to the third wire a current which is in phase oppositionto the vector sum of the currents in the transmission wires. Such an arrangement will effectively neutralize the electric fields produced s a result of the phase unbalance of the currents in the transmission line.

Among the objects of the invention are to provide an improved transmission line in which a conductor is arranged parallel to the conductors of two wire high frequency transmission line and means are provided for applying to the third conductor a, current which is inphase opposition to the vector sum of the currents in the two wire transmission line. Another object of the invention is to provide an improved parallel wire trans mission line for connecting a source of high frequencies to a load including a center tapped half wave line connected across the transmission line at the high frequency source, a second center tapped half wave line connected across the transmission line at the load, and a third parallel wireline connected between the center taps of the respective half wave lines and disposed equidistant from the wires of the parallel transmission-lines. Another object of the invention is to provide an improved means for efiectively neutralizing objectionable radiation from a two wire transmission line connecting a source of high frequencies to a load, which includes a third wire, disposed in proximity to the transmission line and arranged to carry currents in phase opposition to the vector sum of the currents in the two wire transmission line. Still another object of the invention is to provide an improved means for deriving currents in phase opposition to the vector sum of the currents in the two wire transmission llne from the electrical midpoint of lumped resonant circuits connected across the parallel wire transmission line at the high frequency source and the load respectively. Still another object is to provide an improved transmission line including a center tapped inductor connected in parallel with a capacitor, the constants of which provide resonance at the desired frequency, and a second parallel inductor and capacitor, tuned to resonance and grounded at the electrical midpoint, connected between the electrical midpoint of the first inductor and one end of an auxiliary transmission wire.

The invention will be described by reference to the drawing of which Fig. l is a schematic diagram of one embodiment of the invention utilizing half wave lines at the high frequency p ly and Fi 3 is a cross-sectional view of a preferred arrangement of the three transmission wires. Similar reference numerals are ap= plied to similar elements throughout the drawing.

Referring to Fig. 1, a parallel two wire transmission line, comprising the conductors I and 2,

is connected between a high frequency generator 4 and a, load 5. The characteristics of the generator :i and load 5 are not a part of this invention. When the system is utilized for the transmission of extremely high frequencies, a pair of serially-connected conductors I5 and I, each of which are one-quarter wave length long, is connected at its midpoint 9 to one end of a third parallel wire transmission line 3. A second pair of serially-connected quarter wave conductors III and II, is connected across the transmission line. comprising the conductors I and 2, in proximity to the-load 5. The electrical midpoint I 3 of the second half wave line is connected to the remaining end of the third parallel transmission wire mission wire 3, since the currents applied to this 3 in proximity to the load 5. It will be apparent that when the currents in the wires I and 2 of the parallel transmission line are in exact phase op-v position, no current will flow in the third transwire are in phase opposition to the vector sum of the currents in the wires I and 2. Should phase unbalance in the transmission wires l and 2. occur, a current would be applied to the third transmission wire 3 which would effectively neutralize objectionable radiation by the wires i and 2.

Referring to Fig. 2, a lumped resonant circuit comprising the parallel connected inductance I6 and capacitor I1 is connected across the transmission lines I and 2 at the generator t. A second resonant circuit comprising the second parallel connected inductor l8 and the secondcapacitor I9 is connected between the electrical midpoint of the first inductor I6 and one end of the third transmission line 3. The electrical midpoint of the second inductor I8 is connected. to ground. Similarly connected lumped resonant circuits comprising a. third center tapped parallel conne ted inductor 26 and a third capacitor 21,

and a parallel connected iourth inductor ll and a fourth capacitor 29 are connected across the transmission lines I- and 2 in proximity to the load and to the center tap of the inductor 28 and the remainingend oi the thirdtransmission wire 3 respectively. The electrical midpoint oi the fourth inductor 28 is connected to ground.

The circuit of Fig. 2 operates in essentially the same manner as the circuit oi Fig. 1 but the former isjbetter. adapted from a constructional standpoint to frequencies below the ultra, high frequency spectrum.

Fig. 3 indicates the relative arrangement of the three wires l, 2 and 3 of the transmission line for most effective neutralization oi. radiation normally caused by current phase unbalance occurring between the currents in the conductors l and 2 of the parallel two wire transmission line.

It should be understood that this invention is not limited to the specific structure disclosed but that other suitable phasing circuits well known in the art mayb utilized to derive the neutralizing current applied to the third transmission wire 3 for eiIective neutralization of objectionable radiation. It should also be understood that any other suitable physical arrangement of the wires *of the transmission line may be utilized providing suitable neutralizing currents are applied tothe third wire in accordance with the teachings of this invention.

, I claim as my invention: v 1 v 1. In a parallel two wire transmission line for coupling a signal source to. a load and for reducing radiation due to current phase unbalance in the wires of said line including in combination a third parallel wire extending substantially coextensively with said two line wires, means adjacent said source for deriving a neutralizing current in phase opposition to the vector sum'of the currents in said two wire line, means for applying said neutralizing current to said third wire, and means adjacent said load for connecting said third wire to said line in phase opposition to the vector sum of the currents there occun'ing in said two wire line.

2. In a parallel two wire transmission line for coupling a signal source to-a load and for reduc- I ing radiation due to current phase unbalance in the wires of said line including in combination a third parallel wire extending substantially coextensively with said two line wires, means including two series connected quarter wave lines connected across said transmission line adjacent said.

source -for deriving a neutralizing current in phase opposition to the vector sum of the currents in said two wire line, means for applying said neutralizing current to said third wire and means including two series connected quarter wave lines connected across said transmission line adjacent said load for'connecting said third wire to said line in phase opposition to the vector sum of the currents there occurring in said two wire line.

3. In a parallel two wire transmission line for coupling a signal source to a load and for reducing radiation due to current phase unbalance in the wires of said line including in combination a third parallel wire extending substantially coextensively with said two line wires, means including a lumped resonant circuit connected across said transmission line adjacent said source for deriving a neutralizing current in phase opposition to the vector sum of the currents in saidtwo wire line, means for applying said neutralizing current to said third wire and means including a lumped resonant circuit connected acros said transmission line adjacent said load for connecting saidthird wire to said line in phase opposition to the vector sum of the currents there occurring in said two wire line. I

4. In a parallel two wire transmission line for coupling a signal source to .a load and for reducing radiation due to current phase unbalance in the wires of said line including in combination'a third, parallel wire eql'lidlstant from said two wires, and extending substantially coextensively with said two line wires, means adjacent said source for deriving a neutralizing current in phase opposition to the vector sum of the currents in said two wire line, means for applying said neutralizing current to said third wire and means adjacent said load for connecting said third wire to said line in phase opposition to the vector sum 1. of the currents there occurring in said two wire line.

5. The combination of a parallel wire transmission line for coupling a signal 'source to a load, a third parallel wir equidistant from said two wires and extending substantially coextensively with said two line wires, means including two series connected quarter wave line's connected across said transmission line adjacent said source 'for deriving a neutralizing current in phase opposition to the vector sum of the currents in said two'wire line, means for applying said neutraliz ing current to said third wire and means including two series connected quarter wave lines connected across said transmission line adjacent said a load for connecting said third wire to said line in phase opposition to the vector sum of the'currents there occurring in said two wire line,

6. A radiation reduction transmission line including a parallel two wire transmission line for coupling a signal source to a load, a third parallel wire equidistant from said two wires and extending substantially coextensively with said two line wires, means including a lumped resonant circuit connected across said transmission line adjacent said source for deriving a neutralizing current in phase opposition to the vector sum of the currents in said two wire line, means for applying,

said neutralizing current to said third wireand means including a lumped resonant circuit connected across said transmission line adjacent said load for connecting said third wire to said line in phase opposition to the vector sum of the currents there occurring in said two wire line.

7. In a parallel two wire transmission line-for coupling a signalsource to a load, means for reducing radiation due to current phase unbalance in said wires of said line including a third parallel wire equidistant from said two wires and extending substantially coextensively with said two line wires, means including a lumped resonant circuit connected across said transmission line and a second lumped resonant symmetrically grounded circuit connected between the electrical mid-. point or said first lumped circuit and said third wire adjacent said source for deriving a neutralizing currentin phase opposition to the vector sum of the currents-in said two wire line, means for applying said neutralizing current to said third wire, and means including a lumped resonant circuit connected across said transmission line and a second lumped resonant symmetrically grounded circuit connected between the electrical midpoint of said first lumped circuit and said third wire adjacent said load for connecting said thirdwire to said line in phase opposition to the vector sum of the currents there occurringin said two.

wire line.

THOMAS M. GLUYAS, JR. 

